High Temperature Thermal Shock Synthesis of Catalyst-Decorated Nanostructures for Energy Storage

An efficient and ultrafast method to synthesize well-dispersed functional nanoparticles with controlled size and distribution remains largely unanswered. Conventional synthesis methods (wet chemistry, spray pyrolysis, among others) tend to be less controllable, leading to nanoparticle aggregation as well as a wide particle size distribution. Therefore, a short synthesis duration is critical to control nanoparticle size and minimize aggregation. Here we report a rapid and universal high temperature thermal shock method to form and uniformly disperse metallic nanoparticles on a conductive carbon support, such as carbon nanofibers (CNF). First, the desired metal salt precursor is homogeneously mixed into an aqueous solution and loaded onto the conductive carbon support. After drying, the precursor-loaded CNF film is attached to electrical leads inside an argon-filled glovebox to facilitate the electrically triggered Joule heating procedure. An applied electrical pulse from an external power source induces the thermal shock process by heating the precursor-loaded CNF to ~2000 K for mere milliseconds at ultrafast heating/cooling rates (~10 5 K/s). Due to the short high temperature exposure and rapid cooling rate, nearly any precursor metal salt can decompose and nucleate into uniformly distributed metallic nanoparticles with ultrafine particle sizes without damaging the conductive support. Note that kinetic control can also be achieved by tuning the synthesis parameters (pulse duration, heating temperature, heating/cooling rates). Specifically, as the pulse duration increases to seconds, the temporal limitations for diffusion and migration broaden, allowing nanoparticles with larger diameters to form with a wider particle size distribution. In the field of energy storage, nanoparticle-decorated conductive supports are ideal battery electrodes. To demonstrate the proposed manufacturing method, lithium-oxygen (Li-O 2 ) batteries were successfully assembled and tested using the nanocatalyst-decorated CNF films. Bifunctional ruthenium nanoparticles were synthesized by the rapid thermal shock method to increase the electrocatalytic activity of the CNF-based Li-O 2 cathodes and improve oxygen reaction kinetics. The results indicate the potential of this rapid manufacturing method to synthesize an array of non-agglomerated nanoparticle-decorated supports for energy storage devices and beyond.